Hello boraxman!
On 05 Jan 2022, boraxman said the following...
When your BBS polls a hub, and obtains newer messages, how does the
sender know which messages are newer?
It's all a matter of subscriptions -- your hub is subscribed to all echomail areas that you want (have subscribed to), and when it receives a new message (from wherever it came from), it checks which of its downlinks/downstream nodes (e.g. you) that should get a copy, and stores a copy for those in its outbound folders (on disk). So when you poll your hub, the hub simply checks in its outbound folders if there are any files stored for your node, and, if so, delivers those to you, and then removes them.
Best regards
Zip
--- Mystic BBS v1.12 A47 2021/12/24 (Linux/64)
 * Origin: Star Collision BBS, Uppsala, Sweden (21:1/202)